It was caused by a crack in the concrete - narrow, but wide enough to catch and instantly halt Carpenter's front wheel.

He estimates he was travelling at about 20km/h when catapulted forward.

"I recall there being people walking. I had dropped behind Chris for a few seconds while they went past. I moved out to go alongside him again and saw a crack in the concrete. I hit it and it was too late."

Tant, a former firefighter, called an ambulance, tended to his friend's profusely bleeding face with the help of a passing motorist's first aid kit, and flagged down an ambulance that happened to be passing.

Carpenter was taken first to Auckland City Hospital by ambulance and later transferred to Middlemore.

In a stern email addressed to Auckland Transport chief executive Shane Ellison today, Tant said he emailed the organisation's advice line on Sunday about the offending section of footpath.

He followed this up with a phone call to AT early on Monday morning, "stressing the extent of the injuries suffered ... and the urgent need to mark the hazard with at least a couple of road cones and/or some dazzle paint.

"I have had no follow up call and as of last night - three business days later - AT had done nothing to mark this hazard."

He took matters in hand and applied some dazzle paint last night, "so as to give other riders a chance to avoid a similar fate".

Minutes after the Herald approached AT today, Tant reported that an AT staffer had called him to apologise and to assure him it was making an urgent temporary repair with asphalt.

AT later confirmed these actions to the Herald, adding that it was notified of the faulty path by the Albert Eden Local Board on February 11.

"This path was built as part of the Waterview Tunnel project. This work was done by the Well Connected Alliance contracted by NZ Transport Agency," AT said.

"Part of the footpath has moved which has caused gaps; this isn't acceptable and should never have happened."

"We apologise to Mr Carpenter, we should have moved faster to make it safe."